Rotary pump

ABSTRACT

A rotary pump comprises cam surfaces formed on the outer periphery of a pump rotor rotatably mounted in a cylindrical bore in a pump housing, abutments slidably contacting the cam surfaces and spaced at equal intervals about the circumference of the cylindrical bore, and separating a plurality of pump chambers formed within the cylindrical bore, and a flow control valve actuated by the centrifugal force imparted thereto by rotation of the pump rotor to maintain the pump discharge approximately constant.

United States Patent Inventors Tamaki Tomita;

Sadamu Kato; Hideo Mizoguchi, all of Kariya, Aichi, Japan Appl. No. 852,706 Filed Aug. 25, 1969 Patented Aug. 17, 1971 Assignee Toyoda Koki Kabushiki, trading as Toyoda Machine Works, Ltd. Kariya, Aichi Prefecture, Japan Priority Aug. 26, 1968 Japan 43/61093 ROTARY PUMP 9 Claims, 13 Drawing Figs.

417/284 Int. Cl F04c 1/00, F04c 3/00 [50] Field of Search 417/294, 284;418/188,187, 186,214,216; 103/123; 230/149; 123/14; 137/56 5 6] References Cited UNITED STATES PATENTS 3,495,539 2/1970 Tomita et al 103/123 Primary ExaminerCarlton R. Croyle Assistant ExaminerRichard E. Gluck AttorneyHolcombe, Wetherill and Brisebois ABSTRACT: A rotary pump comprises cam surfaces formed on the outer periphery of a pump rotor rotatably mounted in a cylindrical bore in a pump housing, abutments slidably contacting the cam surfaces and spaced at equal intervals about the circumference of the cylindrical bore, and separating a plurality of pump chambers formed within the cylindrical bore, and a flow control valve actuated by the centrifugal force imparted thereto by rotation of the pump rotor to maintain the pump discharge approximately constant.

PATENTED Mun 7 Ian SHEET 2 OF 8 FIG. 3

FIG, 4

PATENTEDAUBHIQII 3,600,108

' SHEET 5 or 8 FIG. :0

PATENTEUAUBIIIQH SHEET 7 OF 8 FIG. II.

ROTARY PUMP DESCRIPTION or THE INVENTION The present invention relates to rotary pumps which transform the rotary energy of a prime mover into the pressure energy of a fluid, and more particularly to a rotary pump in which a flow control valve actuated by centrifugal force is carried by a pump rotor rotatablymounted in a cylindrical bore and having cam surfaces on its outer periphery, so that the pump discharge may be kept nearly constant even when the r.p.m. of the pump rotor exceeds a specified r.p.m.

An object of the present invention is to provide a rotary pump which achieves a substantial saving in the power required to drive the pump by actuating a flow control valve in response to centrifugal force when the rpm. of the pump rotor exceeds a specified rpm, and thereby connecting the suction side of the pump with its discharge side, so that the bypassing of pressurized fluid from the discharge side to the suction side may be controlled in dependence on the rotor r.p.m.

Generally, in the rotary pumps of vehicles the rotor is driven directly by the engine. Therefore the pump discharge tends to increase with an increase in the r.p.m. of the engine or the rotor.

However, in the high rpm. range of a fluid-pressure pump or under a no-load condition in a fluid-pressure motor supplied by the pump, the necessary flow of a fluid on the load side is small compared with the pump discharge. Accordingly an excessive amount of fluid is discharged in vain without contributing useful work, resulting in a substantial waste of power. For instance, when the fluid-pressure pump is applied to the power steering device by which the steerable wheels of a vehicle are steered under a small manual steering torque as boosted by a fluid-pressure motor, in spite of the fact that the fluid-pressure motor of the power steering device is under practically no-load in the high rpm. range of the engine, i.e., when the vehicle is running at high speeds, the pump is operated at a high speed discharging large quantities of the fluid, and in consequence the practical output of engine drops on account of the wasted power in the pump, thereby degrading the high-speed running performance of the vehicle.

For this reason, there has arisen a demand for a fluid-pressure pump in which the pump power is automatically lowered when an engine is operating at high speeds, in order to save the power wasted in driving the pump and thereby to minimize the loss in the engine output required for high-speed operatron.

In view of this drawback of conventional pumps, the present invention aims at minimizing the loss in engine output consumed in the pump by building a centrifugal force-actuated flow control valve into the rotatably mounted pump rotor, which valve is opened in response to the centrifugal force caused by the rotation of the pump rotor to connect the discharge side of the pump with its suction side and thereby to limit the pump discharge to the necessary level.

Other objects of this invention will become more fully apparent from the following detailed description of several embodiments of the invention with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal sectional view taken through one embodiment of a rotary pump according to this invention;

FIG. 2 is a sectional view taken along the line II-II of FIG. 1; FIG. 3 shows a portion of FIG. 2 on a larger scale; FIG. 4 is a perspective view showing an abutment provided in a cylindrical bore;

FIG. 5 is a sectional view taken along the line V-V of FIG. 1;

FIG. 6 is a perspective view of a pump rotor;

FIG. 7 is a longitudinal section taken through another em bodiment of the rotary pump according to the invention;

FIG. 8 is a sectional view taken along the line VIII-VIII of FIG. 7;

FIG. 9 shows a portion of FIG. 8 on a larger scale;

' FIG. 10 is a longitudinal sectional view taken through yet another embodiment of the rotary pump according to the invention;

FIG. 11 is a sectional view taken along the line XI-XI of FIG. I0;

FIG. 12 shows a portion of FIG. 11 on a larger scale; and

FIG. 13 is a diagram showing the rotor r.p.m. of a rotary pump according to this invention compared with the characteristic curve of its discharge.

Referring now to FIGS. 1 and 2, reference numeral 1 indicates a pump housing, provided with a cylindrical bore 2. A pump rotor 3 is rotatably mounted in the bore 2. On both sides of the pump rotor 3 are inserted discs 4, 5 and outside of the discs 4, 5 are a support 6 and a plug member 7, attached to the housing 1. In the plug member 7 is journaled by means of a bearing 9 one end of a drive shaft 8. The drive shaft 8 extends outwardly from said bearing, through the disc 5, the pump rotor 3, the disc 4 and the support 6 and is journaled by means of a bearing 10 in the support 6. The outwardly projecting end of the drive shaft 8 is coupled to and driven by the output shaft of a prime mover (not shown). The pump rotor 3 is engaged by a key 14 with the drive shaft 8.

The pump rotor 3 constitutes a noncircular cam as will be hereinafter described. In the pump housing II, which receives the pump rotor 3, there is formed a circular inside wall, which defines the above-mentioned cylindrical bore 2. Between the bore 2 and the pump rotor 3 is a crescent-shaped clearance 2a. On the inner wall of the bore 2 are a plurality of radial, circumferentially spaced slots 11, in each of which is an abut ment 12 biassed inwardly by a compressed spring 13. Under the force of each spring 13 each abutment 12 bears uniformly against the outer periphery of the pump rotor 3 and divides the crescent-shaped clearance 2a into a plurality of pumping chambers. In FIG. 2 there are four abutments 12, which form four such mutually partitioned chambers between the bore 2 and the pump rotor 3. As shown in FIG. 4, the abutment 12 is preferably made of sheet metal bent into a channel shape, and has as small a mass as possible so as to follow better at high speeds. On one side of the abutment 12 is a notch 12a, through which the discharged pressure fluid is transmitted to the back of the abutment 12 to urge the abutment toward the periphery of the rotor more positively.

Cam surfaces on the outer periphery of the pump rotor 3 which rotates clockwise create create a suction-discharge cycle in the respective pumping chambers A,--A.,. As shown in FIG. 2, the cam profiles on the outer periphery of the rotor 3 are such that between the cam surface 30 which increases progressively in radius in the direction of rotation, and the cam surface 3d which decreases progressively in radius in the direction of rotation, there are two substantially part-circular cam surfaces 3a, 3b.

The first part-circular cam surface 3b has its center at the center of the drive shaft 8 but has a smaller radius than the bore 2. The second part-circular cam surface 3a also has its center at the center of the drive shaft 8, and has the same radius as the bore 2, being smoothly rotatable in contact with the bore 2.

The transition between the cam surfaces 30, 3b, 3c and 3d are smooth so that there is no sharp change in the curved surface. BEtween the cam surfaces 3c, 3b, 3d and the bore 2 is the crescent-shaped clearance. The part-circular cam surfaces 3a, 3b provide better sealing engagement between the rotor 3 and the abutment 12, since the abutment 12 can follow the radial change of the periphery of the rotor '3 snugly so that the abutment 12 may begin its radial displacement after staying on the concentric portions where there is not any radial change.

In the central portions of the cam surfaces 30 and 3d there are respectively provided recesses l6, 17 at approximately diametrically opposite positions. The recesses 16, 17 respectively extend over approximately one fourth of the circumference and are formed to balance the weight of the rotor 3, which balancing is required. by its eccentricity. At the boundary between the recess 17 and the cam surface 3b is a narrow slot 18 extending toward the part-circular surface 3b from the recess 17.

The slot 18 serves to prevent pulsation of the discharge pressure by gradually transferring the fluid in the chamber in delivery cycle into the chamber which is about to go into delivery cycle.

A suction passage 19 and a discharge passage 20 extend axially of the rotor 3. The suction passage 19 leads via an annular groove 21, a connecting hole 22 and an annular groove 23 on the disc 5 to a suction port 24 communicating with a fluid tank. The suction passage 19 also communicates through holes 25, 26 with the recess 16.

:1 the other hand, the discharge passage 20 leads through an annular groove 27 and a connecting passage 28 cut on the disc 4 to a discharge portion 29. The pressurized fluid coming out of the discharge port 29 is supplied, for instance, to the power steering apparatus of a vehicle. The discharge passage 20 also communicates through holes 30, 31 with the recess 17.

Corresponding to the groove 27 of disc 4 at one end of the discharge passage 20, there is a pressure-balancing groove 32 on the disc at the other end of the discharge passage 20, which balances the fluid pressure acting on both sides of the pump rotor 3.

As shown in FIG. 2, the pump rotor 3 is provided with a radial flow control valve FC. FIG. 3 illustrates the details of this flow control valve FC. In the rotor 3 a valve chamber 35 extends from the outer periphery of the rotor toward its center of rotation. A sleeve 36 is inserted in the chamber 35 and is immobilized by a snap-action ring 37. Two axially spaced annular grooves 38, 39 are cut in the outer surface of the sleeve 36. One of the grooves 38 leads through a passage 33 to the suction passage 19, the other groove 39 leads through a passage 34 to the recess 17 and through the passage 31 to the discharge passage (see FIG. 2).

Axially spaced annular grooves 53, 54 are cut on the inner surface of the sleeve 36 and are respectively connected through connecting passages 55, 56 to the grooves 38, 39. Inside the sleeve 36 is a spool valve 40 which is slidable radially of the rotor 3, in response to centrifugal force caused by the rotation of the pump rotor 3. The spool valve 40 is cup-shaped and provided with a hole 57 normally opening to the groove 54. At the bottom of the spool valve 40 is an orifice 41. The

cup bottom provided with the orifice 41 separates the valve chamber 35 into a first control chamber communicating with the discharge passage 20 and a second control chamber communicating with the suction passage 19. A plug 58 is screwed into the end of the valve chamber 35. Between the plug 58 and the spool valve 40 is a spring 42 which serves to urge the spool valve 40 at all times toward the rotor rotation center. Thus, in the rest state as shown in FIG. 3, the force of the spring 42 causes the spool valve 40 to assume its lower position, at which its flange engages the shoulder of the sleeve 36, thereby closing the annular groove 53 and cutting the communication between the discharge side and the suction side. If, the this state, the pressurized fluid on the discharge side is introduced into the valve chamber 35, the first and second control chambers will of course attain equal pressure.

In the flow control valve FC, an increase in the r.p.m. of the pump rotor 3 will cause centrifugal force to compress the spring 42 and as a result the spool valve 40 will be radially displaced, thereby establishing communication between the discharge side and the suction side with the result that a part of the discharge high pressure fluid from the discharge port 29 is bypassed to the suction side to adjust the pump discharge. Consequently, the higher the r.p.m. of the rotor is, the stronger the centrifugal force exerted on the spool valve 40 becomes and accordingly the area of the groove 53 to be opened by the sliding of the spool valve 40 will be substantially proportional to the rotor r.p.m., increasing the bypass from the discharge side to the suction side in dependence on the rotor r.p.m.

In other words, the pump discharge can be kept approximately constant regardless of the rotor r.p.m. The pump discharge, however, can be set at a desirable level, as described later, through selection of the setting conditions.

Meanwhile, as shown in FIG. 5, there is a built-in pressure relief valve between the discharge side and the suction side. A valve chamber 45 is bored in the plug 7 and a retainer 47 is slidably mounted in this chamber 45 and biassed by a spring 46. On the opposite side to the spring 46, i.e., on the valve chamber side of the retainer 47, is a hole 49 communicating through the passages 48, 48 with the pressure-balancing groove 32, while a hole 50 connects the valve chamber 45 to the suction port 24.

In this arrangement a poppet valve 51 biassed by the spring 46 normally plugs the hole 49, thereby cutting the communication between the suction side and the discharge side. But when the pump discharge pressure overcomes the force of the spring 46, the poppet valve 51 is displaced by the fluid pressure to establish communication between the holes 49 and 50, thereby bypassing pressurized fluid to the suction side, and in consequence preventing the pump discharge pressure from exceeding the pressure set by the spring 46. In this case the pressure to be set by the relief valve can be varied by simply changing the force of the spring 46 by adjustment of a screw 52.

In the rotary pump described above, when the drive shaft 8 is rotated by an external prime mover (say, the engine of a vehicle), the pump chambers A,-A,, are subjected to an alternating suction-discharge cycle and each pump chamber accordingly makes one cycle of pumping action per one rotation of the pump rotor 3. With an increase in the r.p.m. of the rotor 3 the total discharge from the discharge port 29 will rise following the curve 8 in FIG. 33. Meanwhile, with an increase in the r.p.m. of the rotor, the centrifugal force acting on the spool valve 40 will also grow proportionately. When this centrifugal force overcomes the force of the spring 42, that is, when the rotor r.p.m. reaches the point a in FIG. 13, the spool valve 40 will be radially displaced to connect the annular groove 53 (which leads to the suction side) to the valve chamber 35, thereby causing the pressurized fluid to return from the recess 17 on the discharge side via the passage 34, the annular groove 39, the passage 56, the annular groove 54, the hole 57, the valve chamber 35, the orifice 41, the passage 55, the annular groove 38, the passage 33 and the hole 26 to the suction passage 19. As a consequence, as a practical matter, the flow of pressurized fluid leaving the discharge port 29 will not be proportional to the rotor r.p.m., but it will become possible to discharge the fluid from the discharge port 29 at an approximately constant rate as indicated by the curve a of FIG. 13. Thus, only the necessary amount of pressurized fluid will leave the port 29, thereby substantially reducing the power required to drive the pump.

In this case, the timing of the bypass flow from the discharge side to the suction side can be suitably selected by varying not only the rotor r.p.m. but also the mass of the spool valve 40 or the spring force, while the volume of this bypass flow may be arbitrarily selected by adjusting the orifice 41, etc. Flow control as illustrated by the curve B in FIG. 13 is therefore possible.

Moreover, if the pump discharge pressure rises above the specified value, the fluid pressure will overcome the spring 46 to make the retainer 47 slide, thereby bypassing the pressurized fluid from the discharging side to the suction side to hold the discharge pressure below the normally set value, thus increasing as the result the efficiency of the pump suction and further reducing the power required to drive it.

In this way, the pump discharge does not increase with the rotor r.p.m., but can easily be controlled to an approximately constant rate by the action of the flow control valve FC which bypasses an excess of pressurized fluid to the suction side.

FIG. 7 illustrates another embodiment of this invention, which is not basically different from the preceding embodiment except for slight modification of the flow control valve to bypass fluid from the discharge side to the suction side when the r.p.m. of the rotor increases. As shown in FIG. 7, a constriction 61 is provided at the left end of the discharge passage 20. The fluid released through the constriction 61 passes at a lower pressure out of the pump through the discharge port 29, the groove 27 and the passage 28.

As seen in FIG. 8, the pump rotor 3 has a radially extending flow control valve FC. FIG. 9 shows details of this flow control valve FC. In the rotor 3 a valve chamber 35 extends from its outer periphery toward its center of rotation and a sleeve 36 is'fitted in the valve chamber 35. The sleeve 36' contains a slidable spool valve 40, which divides the chamber 35 into two sections, one of which receives a pressurized fluid which is introduced through a passage 62 before passing the constriction 61, the other section receiving the fluid which is introduced through passages 63, 64 after being released at a lower pressure through the constriction 61. Two fluids with different pressures act on the two sides of the spool valve 40, while a compressed spring 42 is seated on the low pressure side of both sections to bias the spool valve 40 toward the center of rotation of the rotor.

In this arrangement, when the centrifugal force acting on the spool valve 40', which force increases with an increase in the r.p.m. of the rotor, overcomes the force of the spring 42 minus the pressure difference between the two fluids acting on both sides of the spool valve 40', i.e., the force pressing the spool valve 40' toward the center of rotation of the rotor, the spool valve 40' will be displaced in a radial direction to connect the discharge passage 20 to a connecting hole 65 which leads to the recess 16 on the suction side, thereby bypassing fluid from the discharge side to the suction side. In this arrangement, since the bypassing of fluid from the discharge side to the suction side through the flow control valve FC takes place only through a variable orifice formed by relative displacement of spool valve 40 and sleeve 36','it is easy to let a substantial quantity of fluid bypass from the discharge side to the suction side. In FIG. 13, the curve 8 from a point illustrates the relation between rotor r.p.m. and pump discharge in this embodiment. Of course, even in this case, any desired pump discharge control may be provided by adequate selection of the above-mentioned setting conditions.

FIG. 10 illustrates still another embodiment of this invention, in which the pump itself is equipped with a fluid tank. In FIGS. 10, 11, a drive shaft 8 has a relatively large axial suction passage 19. One end of the passage opens into a fluid tank 71 fixed to the pump housing 1 which constitutes the pump body and the fluid is sucked in at this end.

The pump rotor 3 isvkeyed to the drive shaft 8 and a recess 16 is bored in the outer surface of the pump rotor 3. The recess 16 communicates with the suction passage 19'. Almost diametrically opposite to the recess 16 is a similar recess 17', which opens into a discharge passage 20' in the outer periphery of the drive shaft 8' intermediate its ends, the discharge passage 20' being connected to the discharge port 29 through a recess 72 in disc 4' and a recess 73 in support 6'. in the cylindrical bore 2 in the pump housing 1, slots H are cut radially at certain intervals about its circumference and each slot l1 receives an abutment 12, which is uniformly biassed by spring 13 against the outer surface of the pump rotor 3. In FIG. 1 1 six abutments 12 are shown and they divide the crescent-shaped clearance formed between the cylindrical bore 2 and the rotor 3 into six pumping chambers. Reference numeral 74 indicates a lid through which fluid tank 7ll is filled with fluid.

In the pump rotor 3 as seen in FIG. 11 there is a radially extending built-in flow control valve FC. The flow control valve PC is, as indicated in detail the FIG. 12, composed entirely of the same valve components as in the first embodiment, illustrated in FIG. 3. The spool valve 40 in the rest position is locatedat the right extreme so that its flange may engage the shoulder of the sleeve 36 under the pressure of spring 42, thereby cutting the connection between the discharge side and the suction side. With an increase in the r.p.m. of the rotor, however, the spool valve 40, acting under the pressure of centrifugal force, is displaced in a radial direction against the resistance of spring 42, thereby establishing a connection between the discharge side and the suction side to cause bypassing of the fluid from the recess 17 at the discharge side through a passage 66, the control valve FC and a passage 67 to the recess 16 at the suction side, with the result that the volume of pressurized fluid leaving the discharge port 29 can be controlled at a necessary level.

In this arrangement, since the pump itself is equipped with the fluid tank 71 and the suction passage 19 of relatively large bore directly opens into the tank 71, the fluid can be sucked up from the tank 71 against an extremely small channel resistance and, unlike the embodiment in which the suction port is connected through a pipe to the fluid tank, there is a great advantage with respect to power loss, etc.

As described in detail in the above, in view of the tendency of the discharge volume to rise with an increased r.p.m. of the rotor, in this invention, in order to keep the pump discharge nearly constant, regardless of whether the vehicle is running at high speed or low speed, the pump rotor is equipped with a built-in flow control valve containing a movable spool valve which is displaced in response to the centrifugal force caused by the pump rotor. Acc0rdingly, when the rotor r.p.m. exceeds the specified value, centrifugal force causes the flow control valve to act to establish communication betweenthe discharge side and the suction side, thereby bypassing the pressurized fluid to the suction side and in consequence keeping the discharge volume practically constant. By utilizing the fact that when a vehicle is running at high speed its power steering device needs very little power, it is easily possible to use the flow control valve to decrease the pump discharge pressure when the r.p.m. of the rotor increases. By appropriate setting of the spring force acting on the spool valve of the flow control valve, or the means of the spool valve, or the effective orifice, it is possible to vary the flow control characteristic arbitrarily.

Thus, according to this invention, the power consumed by the pump can be greatly reduced. The wasteful loss in the power of a prime mover can be minimized. Particularly, when applied to the power steering device of a vehicle, a rotary pump according to this invention will be given full play with maximum efficiency.

It goes without saying that the present invention is not confined to the illustrated embodiments and that it may be modified by any man skilled in the art within the limits defined by the following claims without thereby departing from the basic principles of the invention.

What we claim is:

1. A rotary pump comprising a pump housing defining a cylindrical bore, a pump rotor rotatably mounted in said cylindrical bore and defining a crescent-shaped clearance between said rotor and said cylindrical bore, said rotor being provided with diametrically opposite first and second cam surfaces concentric with the axis of rotation of said rotor but having different radii, and third and fourth cam surfaces which are located between said first and second cam surfaces and have first and second recesses in communication with suction and discharge passages respectively, a plurality of radial slots in the inner surface of said bore and spaced at equal intervals about the circumference of said bore, an abutment slidably seated in each slot and resiliently urged toward the outer peripheral surface of said rotor, a constriction in said discharge passage to produce a drop in the pressure of pressure fluid passing therethrough, a flow control valve including a valve member slidably mounted in a valve chamber which is connected to said first and second recesses, and spring means for urging said valve member to close a port connected to said first recess, said valve member being urged by the centrifugal force due to rotation of said rotor and the pressure upstream of said constriction to open said port and urged in the opposite direction by said spring means and the pressure downstream of said constriction, whereby said valve member controls bypass flow through said port.

2. A rotary pump as claimed in claim 1, wherein the portion of said discharge passage upstream of said constricted is connected to a pressure relief valve which vents said upstream portion of said discharge passage to said suction passage when the fluid pressure in said discharge passage upstream of said constriction reaches a predetermined value.

3. A rotary pump as claimed in claim 1, wherein each of said abutments is provided with a notch on one side thereof through which pressure fluid is introduced to the back thereof to urge said abutment toward the outer periphery of said rotor.

4. A rotary pump comprising a pump housing defining a cylindrical bore, a drive shaft rotatably mounted in said housing and provided with a suction passage and a discharge passage in the outer peripheral surface thereof, said shaft carrying an eccentric rotor which is rotatably mounted in said cylindrical bore to define a crescent-shaped clearance between said rotor and said cylindrical bore, said rotor being provided with diametrically opposite first and second cam surfaces concentric with the axis of rotation of said rotor but having different radii and third and fourth cam surfaces which are located between said first and second cam surfaces and have first and second recesses in communication with said suction and discharge passages respectively, a plurality of radial slots in the inner surface of said bore and spaced at equal intervals about the circumference of said bore, an abutment slidably seated in each slot and resiliently urged toward the outer peripheral surface of said rotor, and a flow control valve including a valve member which is slidably mounted in a valve chamber in said rotor and separates said chamber into two portions connected to said first and second recesses respectively, said valve member being provided with an orifice connecting said two portions and being resiliently urged to close a port connecting one of said two portions to said first recess, whereby said valve member controls the bypass flow through said orifice as a function of the speed of rotation of said rotor and the pressure differential across said orifice.

5. A rotary pump as claimed in claim 4, wherein the suction side of said pump is connected via the suction passage in said drive shaft to a fluid tank outside said pump housing.

6. A rotary pump comprising a pump housing defining a cylindrical bore, a rotor rotatabiy mounted in said cylindrical bore and defining a crescent-shaped clearance between said rotor and said cylindrical bore, said rotor being provided with diametrically opposite first and second cam surfaces concentric with the axis of rotation of said rotor but having different radii and third and fourth cam surfaces which are located between said first and second cam surfaces and have first and second recesses in communication with suction and discharge passages respectively, a plurality of radial slots in the inner surface of said bore and spaced at equal intervals about the circumference of said bore, an abutment slidably seated in each slot and resiliently urged toward the outer peripheral surtional to the bypass flow through said orifice and movable radially of said rotor to bypass pressure fluid from said second recess to said first recess in response to the centrifugal force applied thereto by rotation of said rotor and the resilient force of spring means positioned to resist said centrifugal force, whereby, one of said two ports is controlled to regulate bypass flow through said orifice as a function of the speed of rotation of said rotor and said pressure differential across said orifice.

7. A rotary pump comprising a pump housing defining a cylindrical bore, a rotor rotatably mounted in said cylindrical bore and defining a crescent-shaped clearance between said rotor and said cylindrical bore, said rotor being provided with diametrically opposite first and second cam surfaces concentric with the axis of rotation of said rotor but having different radii and third and fourth cam surfaces which are located between said first and second cam surfaces and have first and second recesses in communication with suction and discharge passages respectively, a pluralit of radial slots in the inner surface of said bore and space at equal intervals about the circumference of said bore, an abutment slidably seated in each slot and resiliently urged toward the outer peripheral surface of said rotor, and a flow control valve including a valve member which is slidably mounted in a valve chamber in said rotor for movement radially outward of said rotor in response to centrifugal force applied thereto by rotation of said rotor and which separates said chamber by rotation of said rotor and which separates said chamber into two portions connected to said first and second recesses respectively, said valve member being provided with an orifice connecting said two portions and being resiliently urged radially inward of said rotor to close a port connecting one of said two portions to said first recess, whereby said valve member controls the bypass flow through said orifice as a function of the speed rotation of said rotor and the pressure differential across said orifice.

8. A rotary pump as claimed in claim 7, wherein said discharge passage is connected to a pressure relief valve which vents said discharge passage to said suction passage when fluid pressure in said discharge passage arrives at a predetermined value.

9. A rotary pump as claimed in claim 7, wherein each of said abutments is provided with a notch on one side thereof through which pressure fluid is introduced to the back thereof to urge said abutment toward the outer periphery of said rotor. 

1. A rotary pump comprising a pump housing defining a cylindrical bore, a pump rotor rotatably mounted in said cylindrical bore and defining a crescent-shaped clearance between said rotor and said cylindrical bore, said rotor being provided with diametrically opposite first and second cam surfaces concentric with the axis of rotation of said rotor but having different radii, and third and fourth cam surfaces which are located between said first and second cam surfaces and have first and second recesses in communication with suction and discharge passages respectively, a plurality of radial slots in the inner surface of said bore and spaced at equal intervals about the circumference of said bore, an abutment slidably seated in each slot and resiliently urged toward the outer peripheral surface of said rotor, a constriction in said discharge passage to produce a drop in the pressure of pressure fluid passing therethrough, a flow control valve including a valve member slidably mounted in a valve chamber which is connected to said first and second recesses, and spring means for urging said valve member to close a port connected to said first recess, said valve member being urged by the centrifugal force due to rotation of said rotor and the pressure upstream of said constriction to open said port and urged in the opposite direction by said spring means and the pressure downstream of said constriction, whereby said valve member controls bypass flow through said port.
 2. A rotary pump as claimed in claim 1, wherein the portion of said discharge passage upstream of said constricted is connected to a pressure relief valve which vents said upstream portion of said discharge passage to said suction passage when the fluid pressure in said discharge passage upstream of said constriction reaches a predetermined value.
 3. A rotary pump as claimed in claim 1, wherein each of said abutments is provided with a notch on one side thereof through which pressure fluid is introduced to the back thereof to urge said abutment toward the outer periphery of said rotor.
 4. A rotary pump comprising a pump housing defining a cylindrical bore, a drive shaft rotatably mounted in said housing and provided with a suction passage and a discharge passage in the outer peripheral surface thereof, said shaft carrying an eccentric rotor which is rotatably mounted in said cylindrical bore to define a crescent-shaped clearance between said rotor and said cylindrical bore, said rotor being provided with diametrically opposite first and second cam surfaces concentric with the axis of rotation of said rotor but having different radii and third and fourth cam surfaces which are located between said first and second cam surfaces and have first and second recesses in communication with said suction and discharge passages respectively, a plurality of radial slots in tHe inner surface of said bore and spaced at equal intervals about the circumference of said bore, an abutment slidably seated in each slot and resiliently urged toward the outer peripheral surface of said rotor, and a flow control valve including a valve member which is slidably mounted in a valve chamber in said rotor and separates said chamber into two portions connected to said first and second recesses respectively, said valve member being provided with an orifice connecting said two portions and being resiliently urged to close a port connecting one of said two portions to said first recess, whereby said valve member controls the bypass flow through said orifice as a function of the speed of rotation of said rotor and the pressure differential across said orifice.
 5. A rotary pump as claimed in claim 4, wherein the suction side of said pump is connected via the suction passage in said drive shaft to a fluid tank outside said pump housing.
 6. A rotary pump comprising a pump housing defining a cylindrical bore, a rotor rotatably mounted in said cylindrical bore and defining a crescent-shaped clearance between said rotor and said cylindrical bore, said rotor being provided with diametrically opposite first and second cam surfaces concentric with the axis of rotation of said rotor but having different radii and third and fourth cam surfaces which are located between said first and second cam surfaces and have first and second recesses in communication with suction and discharge passages respectively, a plurality of radial slots in the inner surface of said bore and spaced at equal intervals about the circumference of said bore, an abutment slidably seated in each slot and resiliently urged toward the outer peripheral surface of said rotor, and a flow control valve including a valve member which is slidably mounted in a valve chamber in said rotor having two ports connected to said first and second recesses respectively, said valve member being provided with an orifice to produce a pressure differential which is proportional to the bypass flow through said orifice and movable radially of said rotor to bypass pressure fluid from said second recess to said first recess in response to the centrifugal force applied thereto by rotation of said rotor and the resilient force of spring means positioned to resist said centrifugal force, whereby, one of said two ports is controlled to regulate bypass flow through said orifice as a function of the speed of rotation of said rotor and said pressure differential across said orifice.
 7. A rotary pump comprising a pump housing defining a cylindrical bore, a rotor rotatably mounted in said cylindrical bore and defining a crescent-shaped clearance between said rotor and said cylindrical bore, said rotor being provided with diametrically opposite first and second cam surfaces concentric with the axis of rotation of said rotor but having different radii and third and fourth cam surfaces which are located between said first and second cam surfaces and have first and second recesses in communication with suction and discharge passages respectively, a plurality of radial slots in the inner surface of said bore and spaced at equal intervals about the circumference of said bore, an abutment slidably seated in each slot and resiliently urged toward the outer peripheral surface of said rotor, and a flow control valve including a valve member which is slidably mounted in a valve chamber in said rotor for movement radially outward of said rotor in response to centrifugal force applied thereto by rotation of said rotor and which separates said chamber by rotation of said rotor and which separates said chamber into two portions connected to said first and second recesses respectively, said valve member being provided with an orifice connecting said two portions and being resiliently urged radially inward of said rotor to close a port connecting one of said two portions to said first recess, whereby said valve member controls the bypass flow throuGh said orifice as a function of the speed rotation of said rotor and the pressure differential across said orifice.
 8. A rotary pump as claimed in claim 7, wherein said discharge passage is connected to a pressure relief valve which vents said discharge passage to said suction passage when fluid pressure in said discharge passage arrives at a predetermined value.
 9. A rotary pump as claimed in claim 7, wherein each of said abutments is provided with a notch on one side thereof through which pressure fluid is introduced to the back thereof to urge said abutment toward the outer periphery of said rotor. 